EPIDERMAL APPENDAGES. 65 



single-celled hairs, which may be simple or variously branched. 

 The most important of these hairs are those which clothe so 

 abundantly the young roots of most of the higher plants and 

 to which the name of Root-hairs has been applied. These are 

 single cells which have very thin and delicate walls, and are 

 the active agents in the absorption of nutritive matters for the 

 plant. On the above-ground parts the hairs frequently have 

 the terminal cell developed into a secreting cell, carrying 

 gummy, resinous or other products. Such trichoines are 

 known as glandular hairs. 



A good example of simple hairs, which is familiar to every 

 one, is the cotton of commerce. Cotton consists of the hairs 

 on the seeds of the cotton plant. They have been studied in 

 Chapter II. 



HAIRS AND GLANDS AS FOUND ON A GERANIUM. 



Make cross-sections of the young stem of the common 

 Geranium, which need not necessarily be very thin. Mount 

 several in water and examine the circumference of the sections 

 under low power. Two kinds of hairs will be seen, simple and 

 glandular. 



Under high power the simple hairs are very long, consisting 

 of a row of tapering cells which contain transparent proto- 

 plasm and nucleus, easily seen by applying iodine solution. 

 The end cell is long and pointed. The hair fits in among the 

 epidermal cells. The cell-walls are somewhat thick and the 

 cross partitions are well marked. 



There are three kinds of gland hairs. 



One kind is rather long, consisting of a stalk of about six 

 cells (count the actual number), terminated by a larger gland 

 cell, which is round and full of contents. The two or three cells 

 just below the gland cell are suddenly narrowed. On the top 

 of the gland cell there is a crescent-shaped glistening mass 

 which is found to lie in the cell-wall itself between the outer 

 and inner layers. This mass dissolves on applying alcohol or 

 ether, which indicates that it is probably resinous. Additional 

 evidence of this is given by the reaction with alcannin solution, 

 which stains the mass red. The resinous matter is secreted by 

 the gland cell and forced out into the cell-wall where it accumu- 

 lates. Iodine solution shows the presence of protoplasi 

 nuclei in the cells. 



Soak some sections 20 to 30 minutes in strong alcohol, also 



